Haemophilus influenzae synthesizes immune-globulin A (IgA) protease, which enables the bacterium to penetrate and invade the host's respiratory epithelium. This is an example of a bacterium's ability to evade the host:
|A||Cellular or cell-mediated immunity (CMI) against Haemophilus influenzae.|
|B||Nonspecific humoral immunity|
|C||Nonspecific innate immunity|
|D||Specific humoral immunity against Haemophilus influenzae|
a. Immunoglobulin A (IgA) is associated with immunological protection of the host at the epithelial boundary.
b. An IgA protease has the ability to breakdown IgA and thereby act as a virulence mechanism enabling the bacterium to invade the host through an unprotected epithelial boundary.
c. Because IgA is an antibody associated with the humoral (specific) arm of the immune system, IgA protease allows the bacterium the ability to evade the specific humoral immunity of the host.